Sultan Mehmed II conquers Constantinople

For the Ottomans, the conquest of Constantinople had immense symbolic value. The Byzantine capital had withstood numerous sieges by Muslim armies during the Middle Ages, and a saying by the Prophet Muhammad had predicted that a valiant Muslim commander would conquer the Byzantine capital. 

Taking Constantinople meant that the Ottoman dynasty would gain legitimacy and prestige and place itself at the head of the various Muslim empires in the Middle East and Asia. For the young sultan Mehmed II, conquering Constantinople served to consolidate his power against factions in the Ottoman government hostile to his rule.

The siege of Constantinople lasted from early April to late May 1453. The defenders of the city, about 8,500 soldiers aided by contingents of volunteers from various European states, could do little to face the immense Ottoman army, estimated at between 50,000 and 160,000 soldiers.  This army included the famous Janissaries; a corps of elite soldiers recruited from among the Christian subjects of the empire who were taken from their families at a young age, forcibly converted to Islam and educated in the military arts in the schools of the Ottoman palace. 

The Ottomans also had a clear technological advantage: they built powerful cannons, a military innovation of the 15th century with which they could pierce the mighty Roman walls of Constantinople, which had withstood numerous sieges before the invention of firearms. 

The city fell at dawn on May 29, 1453. According to Islamic law, a city that resists the conquest of a Muslim army must:

1. suffer a three-day sacking
2. conversion of places of worship into mosques
3. enslavement of the population, who are divided between the soldiers and the sultan 

This is what happened to Constantinople after the Ottoman conquest. However Mehmed II ordered an end to the sacking and violence one day after the fall of the city, and ordered the protection (from possible destruction) of important civil and religious buildings, such as Hagia Sophia, because he wanted to quickly rebuild the city, which he proclaimed the new capital of the Ottoman Empire.